The measurement of pressures in small cavities is not possible without problems. However, it is necessary in order to determine whether the capping of microsensors is sealed or whether leaks have arisen, for example. Such a seal test is important for all hermetically capped microsensors, such as yaw rate sensors, acceleration sensors, HF-MEMS, etc.
An extremely miniaturized pressure sensor, whose sensor principle is based on a pressure-dependent heat loss of a microbridge, a gap having to exist between the microbridge and a substrate over which the microbridge is formed, is known from “The NanoPirani—Presumably the World's Smallest Pressure Sensor”, Reyntjens, S., De Bruyker, D., Puers, R., TRANSDUCERS' 01, EUROSENSORS XV, 11th International Conference on Solid-State Sensors and Actuators, Digest of Technical Papers/Obermeier, E., Berlin, Germany, Germany: Springer-Verlag, vol. 1, 2001, 2 vol., 1807 pp. 490–3, Vol. 1. The heat is generated via a current flowing through the microbridge and the pressure is determined via a measurement of the electrical resistance of the microbridge.
An integrated microstructure element for detecting thermodynamic variables of a fluid is known from DE 101 23 920 A1. To detect the thermodynamic measured variables of a fluid, a circuit board or a wafer is provided having at least one microstructured heating element which is in contact with the fluid during operation, on which or in whose surroundings a first means for at least temporary application of an alternating current of defined frequency or of a defined frequency band to the heating element and further means for detecting the amplitude of the third harmonic of the electrical voltage applied to the heating element are positioned. The microstructure element shown is especially suitable for determining or monitoring the thermal conductivity and/or heat capacity of a liquid.